Superposition coding was originally used to theoretically prove a channel capacity of a broadcast channel. A principle of superposition coding is; information to be transmitted is layered into a plurality of streams, in which a first stream is transmitted at a largest power; a second stream is transmitted at a second largest power, and so on. The plurality of data streams are superposed to be transmitted simultaneously at a transmitter. A receiver far from the transmitter or a receiver with a poor channel can receive first several streams, while a receiver near the transmitter or a receiver with a good channel can receive all the streams. Therefore, the transmitter can provide service for a plurality of receivers with various qualities of signal receiving, and can provide various data rates according to conditions or channels of the receivers, so as to improve throughput.
A common scenario of superposition coding is that: a base station transmits high power data streams to remote users, and simultaneously sends low power signals to proximal user equipment; in a space for transmitting signals of the base station, the low power signals and the high power streams are multiplexed to use a same space; a remote user detects only high power data streams, while a proximal user equipment detects and eliminates high power data streams at first, and then detects low power signals. In the prior art, to detect high power data streams, the number of antennae for a proximal user equipment has to be more than or equal to a total number of the high power data streams. This condition can not be met in many cases (especially for multi-user multi-input-multi-output (MIMO)).